1. Field of the Invention
The present invention relates to a plasma processing apparatus, particularly a plasma processing apparatus that can improve the uniformity of a processing surface of a wafer.
2. Description of the Related Art
A microwave plasma processing apparatus having a magnetic field for etching, for example, introduces a microwave into a decompression chamber through a wave guide and a cavity resonator, generates plasma in the chamber using interaction of the introduced microwave with a magnetic field produced by a magnetic field-producing coil, and etches processing objects, such as a wafer.
In general, the frequency of a microwave is 2.45 GHz and the microwave travels, in a circular TE11 mode, through the wave guide and is introduced into the chamber. The electric field of the microwave of the circular TE11 mode is distributed in an elliptical shape, as disclosed in ‘Microwave Engineering’ by Nakajima Masamitsu, published by Morimoto Publishing Co. Ltd. In 1975 (in P67). Further, a vacuuming unit that vacuums the chamber, as disclosed in JP-B No. S62-53920, is connected with an exhaust duct disposed under the chamber to extract gas only from one side of the exhaust duct. In this configuration, even though process gas is uniformly introduced into the chamber by a shower plate disposed above the chamber, biased flows of the gas are caused on a wafer.
As described above, since the strength of the electric field of the microwave of the circular TE11 mode is distributed in the elliptical shape, the plasma is correspondingly distributed in an elliptical shape. Therefore, there is a problem in that the etching rate is distributed in the elliptical shape. Meanwhile, in JP-B No. S62-53920, it is disclosed to improve the uniformity in a process by rotating the microwave electric field using a dielectric plate.
Further, the biased flows of the process gas on the waver by the exhaust only from one side is disclosed in JP-A No. 2005-101598, in which it is disclosed to improve the problem of biased flows of the process gas on the wafer by disposing a vacuuming device under a chamber and extracting the process gas uniformly. Further, in this example, the microwave is not introduced into the chamber through a circular wave guide, but a UHF wave is introduced into the chamber through a coaxial wave guide.
FIG. 9 is a vertical cross-sectional view of a plasma processing apparatus in the related art. As shown in FIG. 9, a microwave having a 2.45 GHz wave radiated by a magnetron 1 is transmitted, in a rectangular TE10 mode, into a rectangular wave guide 2 through an isolator, a power monitor, and a matching box 3, which are not shown in the figure. The microwave is further transmitted, in a circular TE11 mode, into a circular wave guide 41 through a spherical-rectangular transducer 21 and then introduced into a chamber 8 through a cavity resonator 5, a quartz plate 6, and a quartz-made shower plate 7.
The process gas for etching flows through a gas pipe 9 through a mass flow controller, which is not shown in the figure, and passes between the quartz plate 6 and the quartz-made shower plate 7, and the introduced into the chamber 8 through a gas hole of the quartz-made shower plate 7. The process gas that has flowed in the chamber 8 is decomposed and plasma is made by interaction of the microwave with the magnetic field while the inside pressure of the chamber 8 is adjusted by an exhaust speed-varying valve 10. The process gas in the chamber is discharged by a vacuuming device 14 through an exhaust duct 12, an on-off valve 13, and the exhaust speed-varying valve 10 disposed at a side of a wafer-placing electrode 11.